1. Field
Certain aspects of the present disclosure generally relate to wireless communications and, more particularly, to a method of generating a unified feedback framework for Multi User Multiple Input Multiple Output (MU-MIMO) enhancement based on indication of a preferred precoder pairings.
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, Long Term Evolution Advanced (LTE-A) systems and Orthogonal Frequency Division Multiple Access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-input single-output, multiple-input single-output or a multiple-input multiple-output (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system supports both time division duplex (TDD) and frequency division duplex (FDD) operation. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle may allow the estimation of the forward link channel from the reverse link channel. In both FDD and TDD systems, a feedback sent from the user terminal may be used among other methods to convey channel state information to a base station. The channel state information at the base station enables it to extract transmit beamforming gain on the forward link when multiple antennas are available at the base station.
Multi User Multiple Input Multiple Output (MU-MIMO) enhancements are being considered as an important aspect of LTE Release 10. As such, improvements to feedback reporting have extensively been studied, and it was shown that accurate feedback reporting can be one of the key enablers for efficient MU-MIMO operation and dynamic Single User/Multi User (SU/MU) switching. An important aspect of these studies was to determine whether or not MU-MIMO operation should be facilitated through additional feedback reports, or whether Single User Multiple Input Multiple Output (SU-MIMO) reporting of precoding matrix information (PMI) provides sufficient performance.